1. Field of the Invention
This invention relates to a method of fabricating a group III nitride semiconductor single crystal, and a method of fabricating a group III nitride semiconductor single crystal substrate. Particularly, the invention relates to a method of fabricating a high-quality group III nitride semiconductor single crystal, and a method of fabricating a group III nitride semiconductor single crystal substrate.
2. Description of the Related Art
Conventionally, a method of fabricating a plurality of gallium nitride (GaN) substrates by a high speed growth or a multiple growth of the GaN, or a method of cutting out a plurality of the GaN substrates by growing a thick bulk ingot and cutting the grown bulk ingot (hereinafter referred to as “bulk method”) and the like are investigated. The bulk method is an expected technique in terms of being capable of fabricating a substrate having C-face and crystal planes other than the C-face.
Further, as a method of fabricating GaN which uses seed crystals having a plurality of faces such as the C-face and crystal planes other than the C-face, a method of fabricating nitride semiconductor crystal is known, the method using seed crystals configured to have a structure that the surface has at least the C-face and the faces directly adjacent to the C-face are not M-face and not A-face (for example, refer to Patent Literature 1).
According to the method of fabricating nitride semiconductor crystal described in Patent Literature 1, since the seed crystals is ground by using a file and the like so as to have a result that the faces directly adjacent to the C-face are not M-face and not A-face, adhesion of polycrystal to a boundary line between the C-face and other faces can be avoided.
Further, it is known that a GaN ingot with no cracks having a thickness of almost 5.8 mm and a diameter of 2 inches in case of a relatively slow crystal growth speed of almost 100 μm/h can be fabricated by using Hydride Vapor Phase Epitaxy (HVPE) method (for example, refer to Non Patent Literature 1).
Patent Literature 1: JP-A-2007-314357
Non Patent Literature 1: S. Kubo et al. “Bulk GaN crystals grown by HVPE”, 2nd International Symposium on Growth of III-Nitrides (2008), publication number: I-Tu-5
However, in case of the method of fabricating nitride semiconductor crystal described in Patent Literature 1, at the first growth the adhesion of polycrystal to the boundary line between the C-face and other faces can not be avoided even if the ground seed crystals are used. Further, it is difficult to grind the seed crystals by using a file and the like while changing the grinding conditions in case of GaN being hard to be ground so as to have a result that the faces directly adjacent to the C-face are not M-face and not A-face, and simultaneously, mechanical damages may remain in the seed crystals by the grinding work. And, it is required that the grinding and the crystal growth using the seed crystals after the grinding are repeated, so that the production cost can not be reduced.
Further, in case of the technique described in Non Patent Literature 1, if the crystal growth is carried out at the crystal growth speed which is elevated higher than 100 μm/h, fine cracks occur in the GaN ingot grown and obtained, so that the surface of the GaN ingot obtained may be roughened.